Chapter 5

Masonry and Earth-Based Materials

Important progress is occurring in the decarbonisation of earth-based masonry, including through the use of low-carbon binders, secondary cementitious materials and admixtures that result in higher-quality products. However, scaling the adoption of these materials affordably relies on local adoption of existing standards, certification (low-carbon credits) and coordinated upskilling of stakeholders.

Decarbonisation of the buildings and construction sector requires a shift away from the use of conventional high-carbon, non-renewable building materials and towards the use of renewable and bio-based materials. However, it is unrealistic to assume that the sector can rapidly and easily transition to 100 per cent renewable biomaterials. During the interim period and beyond, it is critical to support the continued use of lower-carbon non-renewable materials such as masonry and earth-based materials.

Figure 5.15 Climate types and the potential for earth-based buildings

Earth-based buildings have high potential to reduce emissions in arid and temperate climates.

Note: The figure shows the climate types where earth-based buildings have potential to drive down operational carbon through effective passive design. Source: Gupta 2019.

Traditional Technologies Have Proven Benefits But Have Lost Appeal in Emerging Markets

For much of human history, people have used earth-based materials for load-bearing applications in masonry construction, with sustainable, low-carbon methods. In the traditional context, these materials are made on-site by mixing clay-rich soil, natural fibres, and water, and letting them dry in high outdoor temperatures. Recycling of non-fired earth-based materials is common practice, as the clay binders can be re-used without additional heating or chemical treatment.
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Due to their high thermal mass, earth-based materials can have positive benefits for passive space conditioning, greatly reducing the operational carbon of buildings in certain regions, particularly arid climates (see Figure 5.15). Given the projected impacts of climate change in regions characterised by extremely high day temperatures (above 40 degrees Celsius) and cold nights, passive earth-based systems could help mediate harsh climatic patterns.

Only around 8-10% of the world’s people currently live in earth-based structures.

At the end of the 20th century, earth-based structures housed around a third of the global population; since then, this share has fallen to only 8-10 per cent, with 20-25 per cent of the use occurring in developing countries (Houben and Guillaud 1994; Marsh and Kulshreshtha 2022). As incomes have risen and access to concrete masonry has increased, the use of earth as a building material has declined. Countries where more than 10 per cent of the population still lives in earth-based buildings include Bangladesh, the Democratic Republic of the Congo, Ethiopia, India, Mexico, Nigeria, United Republic of Tanzania and Viet Nam (Marsh and Kulshreshtha 2022).
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In many developing countries, earth-based masonry is associated with poor durability, poor moisture performance, high maintenance and low social class. Inappropriate use of the material for the local context has influenced perceptions. Poor building orientation, large west-wall surface areas and poor cross-ventilation can bring inefficiencies in heat gain/loss. However, across regions, and within high-end architectural design, there is renewed interest in innovating earth-based practices with contemporary techniques and standards.

Earth brick production can be very low carbon, but it is at risk for poor on-site labour and environmental conditions.

Although the potential is high to increase development of locally based supply chains, the production of earth-based materials can have negative social impacts if not properly overseen. Brick is one of the most-used materials at risk for forced labour, with more than 20 countries identified for abuses within the industry (Grace Farms Foundation 2022). Children and adults producing bricks are often held in debt bondage and breathe hazardous dust for prolonged periods.

Figure 5.16 Comparison of the carbon intensity and mechanical performance of different stabilised earth masonry technologies

Stabilisation of earth masonry using Portland cement multiplies the carbon intensity index.

Source: Adapted from Van Damme and Houben 2018.

Emissions from Earth-Based Technologies Rise with Cement-Based Mortars

To improve the performance and durability of earth masonry, progress has been made in developing low-carbon binders, surface treatments and admixtures (chemicals used to reduce binder and water demand and increase durability) (Van Damme and Houben 2018). Traditionally, material stabilisation has been achieved using earthen plasters and stuccoes that integrate a range of plant-based resins, gums, plant juice, animal dung and fluids. More recently, the use of Portland cement to stabilise earth blocks greatly drives up emissions, with only minor performance benefits that can also be achieved through low-carbon, circular by-products (see Figure 5.16). Thus, the carbon footprint of earth-based building technologies varies depending on the binders, natural fibres and additives used; on where production occurs (on- or off-site); and on the use of compaction or firing to improve material strength and durability.

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For non-fired adobe earth blocks that cure in the sun (made from sand, clay binder and organic material), the embodied carbon can range between 1.2 and 5.4 kilograms of CO2 per kilogram of earth block (Illampas, Ioannou and Charmpis 2014; Christoforou et al. 2016).

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For fired clay bricks, the carbon footprint skyrockets due to the high temperatures required for clay sintering. When using a natural gas-fired kiln, the average carbon footprint is an estimated 230-250 kilograms of CO2 per kilogram of earth block (Kulkarni and Rao 2016). The footprint using an oil-fired kiln is 1.4 times higher, near 340 kilograms of CO2 per kilogram of earth block (Venta and Eng 1998).

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For rammed earth wall structures – in which processed earth soil is compacted into solid walls using temporary formwork – the use of Portland cement stabilisers and electric and pneumatic ramming can greatly increase carbon footprints (Reddy and Kumar 2010). Compared to conventional concrete masonry, adding 5-10 per cent Portland cement and lime to rammed earth structures led to higher CO2 emissions and worse performance (Scrivener, John and Gartner 2018). The carbon footprint of stabilisation techniques must be weighed against the susceptibility of unstabilised earth walls to mechanical and moisture damage and erosion.

Interest in Modern Earth-Based Construction Is Gradually Increasing

Globally, the stock of modern earthen buildings is growing.

Due to the high quality and appeal of modern earthen buildings, the use of local earth resources for building is gaining recognition as a “niche,” reliable and attractive option (Swan, Rteil and Lovegrove 2011; Niroumand et al. 2017). As a consequence, the number of innovative earth-based products from earth construction companies has increased (Leylavergne 2012; Marsh and Kulshreshtha 2022), as has the worldwide stock of modern earthen buildings (Correia, Dipasquale and Mecca 2011). However, such initiatives are limited by the high costs of entrepreneurial experimentation and early adoption shouldered by clients.

KEY STEPS TOWARDS

Decarbonizing Earth-Based Masonry

Improve the design of earth-based masonry for longevity, and provide technical training

In the near term, effort is needed towards improving the longevity of earth masonry without Portland cement (Scrivener, John and Gartner 2018).

Technical training is needed on the design to enhance the durability of earth masonry and panel systems.

On-site training and upskilling of architecture, engineering and construction professionals is needed to encourage and normalise the design and integration of earth-based technologies.

Shift from Portland cement binders to low-carbon alternatives in earth-based masonry

Rapid development is needed of low-carbon binders, natural supplementary cementitious materials.

Promote alternatives to Portland cement for binders, such as low-carbon lime, alkaline-activated materials, and geopolymers, including volcanic pozzolan (Abid et al. 2022; Kamwa et al. 2022).

Promote bio-based supplementary cementitious materials including fused laterite and agricultural and industrial residues, often available locally (Adinkrah-Appiah and Obour 2017; Schmidt et al. 2021).

In developing countries where low-carbon binders and cementitious supplements already exist, incentives and education are needed to stimulate market demand and financing to scale adoption (see Box 5.3).

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Develop locally adapted standards to increase adoption and affordability of earth-based masonry

Incentivise stakeholders to continue to develop regional and international standards for earth-based materials that can be integrated into local and regional building codes and material standards (CRAterre-EAG 1998; New Zealand Standards 1998; Vyncke, Kupers and Denies 2018; Africa Research and Standards Organisation 2018; Schroeder 2018).

Increase education and demonstration to boost societal and industry acceptance of earth buildings

Incentivise professionals to develop awareness among clients and to build the research capacity to address negative perceptions and technical challenges.

To incentivise the adoption of low-carbon, earth-based materials, education on their positive impacts needs to be extended to building owners as well as finance and insurance companies.

Education on the appropriate design and integration of earth-based materials is critical for reducing operational carbon, especially for housing in tropical rainforest and savanna climates.

Figure 5.17 Compressed earth block masonry wall and on-site manufacturing in Dakar, Senegal

Senegal is experimenting with typha weed biomass to develop earth-based structures.

Credit: Worofila

Box 5.2

Greening the masonry value chain in West Africa

With their young populations and growing need for infrastructure and housing, developing countries in Africa represent the future in concrete masonry demand. West Africa has traditionally imported most of the clinker and cement that it uses for concrete production, due to the lack of suitable limestone reserves. Given the high carbon footprint of concrete masonry structures that rely on Portland cement binders, however, the development and adoption of local, low-carbon alternatives is key.
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Ghana has the highest use of Portland cement in sub-Saharan Africa, at 215 kilograms per person (Harder 2021). Across West Africa, reducing import dependence through substitution of Portland cement with earth-based, locally available cementitious materials and pozzolana resources will be key to driving down CO2 emissions and increasing economic resilience (Bediako, Amankwah and Adobor 2015). Already, leading cement companies in Ghana, such as SUPACEM and Pozzomix Cement, are using calcined clay cement as an alternative to clinker-based cement.

Adobe earth masonry technologies have a long history in West Africa. They are traditionally made from ubiquitous laterite soils comprising sand, clay, silt, and pebbles, sometimes mixed with cow dung or fibre from guinea grass straw. The modern version of adobe is the compressed earth brick, produced using chemical stabilisation and compaction to improve mechanical performance. Earth masonry is based on community-specific knowledge as well as small-scale industrial manufacturing of stabilised earth block products.
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For countries that supply West Africa with cement, such as Senegal, using low-carbon fuels in production and integrating earth-based masonry products into the value chain is critical. One of Senegal’s largest cement companies, Sococim, is using alternative fuels such as groundnut hulls. Senegal is also experimenting with using typha aquatic weed biomass to develop earth masonry walls and roofing products on-site (see Figure 5.17).